This invention relates to the retention of molded convoluted boots on axles and shafts, such as associated with constant velocity joints.
In U.S. Pat. No. 4,786,272 issued Nov. 22, 1988 to Baker, there is disclosed a blow-molded convoluted boot for use with constant velocity joints. As discussed in that patent, constant velocity or CV joints, as used on automotive drive axles, such as on front wheel drive cars, are commonly enclosed within a convoluted elastomer boot. Such convoluted boots, that is, boots having a plurality of axially spaced annular convolutions, are commonly formed with a small end which is retained by a clamp on the drive shaft leading out of the joint, and a large end clamped to an annular surface of the body of the CV joint. Such boots provide a seal for the joint over the operating range of the constant velocity joint, which may include drive offset angles from between 0.degree. up to 40.degree. or more between the shaft and the joint body. Formerly such boots have been molded of rubber, which may have a hardness in the range of Shore 65A, for example, which permits the boot to flex with the flexing of the joint.
More recently, blow molded boots formed of more rigid thermoplastic polyester elastomers have come into use as a substitute for the rubber boot, by reason of the greater mechanical and physical strength of such elastomers over a wide variety of operating conditions, and generally by reason of the greater toughness of such elastomers and their ability to resist puncture or tearing. However, such blow molded polymers are considerably harder and stiffer than their rubber counterparts, and may, for example, have a hardness in the range of Shore 50D and a flexural modulus of 18,009 psi or more (at 22.degree. C.).
Typical materials from which blow-molded convoluted boots have been made are commonly referred to as thermoplastic elastomers (TPE) and include polyester, polyether, polybutylterephthalate compounds (PEEBT). Typical thermoplastic elastomer materials which are used for blow-molding convoluted boots, as defined above, include du Pont "Hytrel", HTG-5612 and Monsanto's "Santoprene" thermoplastic rubber, typically grade 103-40.
A particular difficulty arising in the clamping and sealing of the respective ends of the boot to the shaft or housing, as the case may be. For example, some instance that the small boot end or neck have a diameter sufficiently greater than that of the shaft over which it is received, for the purpose of clearing objects mounted on the shaft, such as an encircling clip on the shaft. Thereafter, it becomes necessary to provide a means for clamping the boot to the shaft.
Due to the relatively high modulus of the boot material, when a side load is applied to the boot, such as during angulation, or in other installations, during axial movement of the shaft itself, it has been found quite difficult to provide a seal therebetween. Previously, when the boot itself was made of rubber material, it was a relatively simple matter to clamp the boot to the shaft or housing, as the case may be, by compressing the same with a stepless encircling clamp. Typical boot camping arrangements are shown in Burckhardt, U.S. Pat. No. 3,511,061 issued May 12, 1970 and Ukai et al, U.S. Pat. No. 4,360,209 issued Nov. 23, 1982.
Occasionally, an intermediate spacer member or bushing may be inserted between the neck of the boot or bellows and the shaft or housing, as shown in Gehrke, U.S. Pat. No. 4,224,808 issued Sept. 30, 1980. In Gehrke, a split bushing is formed with interfitting tongues and grooves, and is positioned between the neck of the boot and the shaft. Gehrke's intermediate bushing operates as a vent sleeve and forms a spiral opening between the shaft and the sleeve for venting the interior of the boot. The interfitting tongues allow the sleeve to be collapsed about the shaft, are not configured to form a positive seal.
In Brown et al, U.S. Pat. No. 4,767,381 issued Aug. 30, 1988, a partially split sleeve 40 is threaded over the neck of the boot between the clamp and the boot neck and is compressed by the clamp for the purpose of retaining the boot in locked position on the housing of a constant velocity joint.
Sealing bushings or annular members which are softer than the boot itself and which are thus easily crushed by clamping the boot down onto the shaft are satisfactory unless high axial loads are interposed between the shaft and the boot or, in the case of the joint housing, between the housing and the boot. When an axial stress is applied, low modulus elastomers allow the boot or bellows to elongate the softer bushing in the axial direction, and this tends to decrease the outside diameter of the bushing and eventually allows the boot itself to begin to shift and roll or slide off of the bushing. The problem is particularly exacerbated where it is necessary, as previously mentioned, to provide a boot with a neck inside diameter substantially greater than the outside diameter of the body on which it is mounted, for the purpose of facilitating assembly. The gap must be filled by a bushing which provides the dual function of accurately locating and positioning the boot or bellows on the body or the shaft and forming a grease-tight seal with a high degree of integrity.